The present invention relates to the recovery of raw rubber compounds used for recycling and/or reprocessing, from the extruded faulty products or waste (scrap), which are produced during the manufacture of reinforced rubber hoses or tubes for the automotive and other industries, and more particularly to a process for recovering raw rubber compound from semi-finished, reinforcement containing technical rubber products, especially hoses (tubes), before crosslinking (vulcanizing) the same. The invention also relates to equipment for implementing this process.
Recently, unvulcanized, raw rubber compounds have been recycled from scrap, produced during extrusion or calandering, only if the scrap does not contain any reinforcement. Scrap raw rubber containing reinforcement is not suitable for further processing (by extrusion or calandering, also known as procuring), because the rubber compound becomes elasticized and bonds to the reinforcement due to heat transfer during the procuring process.
Currently, there are no known methods for recovering unvulcanized rubber scrap formed during the manufacturing process, although there are several known methods for recovering rubber from vulcanised end-products. Manufacturers usually recycle the unvulcanized rubber after milling it in ripped two roll mills or cutting it in shredders into particles having an average particle size of smaller than 10 mm.
The resulting material can be used for the production of technical rubber products, rubber sheets and solid rubber tires, as secondary raw material having a high (42-45%) rubber content (see Gumiipari Kezikonyv, 2nd Volume, TAURUS-OMIKK, Budapest, 1989).
It should be understood, that the above methods can not be used for producing reinforced, straight or specially shaped rubber hoses (used in the automotive industry for water and oil hydraulic and gas hoses), since the recovered material can not be admixed with the new raw rubber compound used in manufacturing hoses. The use of such textile containing raw material is not acceptable, because the working conditions of the product the stresses on the product, further the manufacturing requirements do not allow it.
Therefore, recycling of reinforced rubber from the scrap produced during or before procuring has not been possible.
The above technical problem results in unnecessary raw material, transport and waste disposal costs for manufacturers, and it also creates environmental problems, as produced scrap is not practically biodegradable, and thus, pollutes the environment.
Furthermore, during manufacturing of such rubber products, the estimated amount of reinforcement containing scrap or waste produced during the extrusion (calandering) step, is about 2-15% of the weight of the end-product. Therefore, there is a great need for a process which recovers recyclable raw rubber compound from unvulcanized, reinforced rubber scrap.
A process has been disclosed in DE 3137502 for recycling of vulcanized and unvulcanized rubber scrap. According to this process, the compounds containing such materials are exposed to heat in boiling hydrocarbon solvents, under pressure and under inert atmosphere. The product obtained by this process can be used as plasticizing agent or demulcent for rubber compounds. However, this process is not suitable for recovering recyclable raw rubber compound from unvulcanized, reinforced rubber scrap.
Accordingly, the aim of the present invention is to provide a method for recovering raw rubber compound from unvulcanized, reinforced rubber compounds.
The present invention involves a process for recovering raw rubber compounds from unvulcanized reinforced, semi-finished technical rubber products. In one embodiment of the invention the process comprises pressing the rubber products between metal surfaces heated to a temperature from 50 to 300xc2x0 C., thereby causing elasticized rubber to flow out; and cooling the elasticized rubber to ambient temperature.
In another embodiment of the invention the process comprises preheating the rubber products to a temperature from 50 to 300xc2x0 C.; pressing the rubber products between metal surfaces, thereby causing elasticized rubber to flow out; and cooling the elasticized rubber to ambient temperature.
The present invention also involves equipment for carrying the above process. The equipment comprises a preheated or forewarmed space, and rolls in close proximity to the preheated space, the rolls rotating preferably at the same speed, but in opposite directions. The equipment has means for the adjustment of the gap between the rolls, drive means for the rolls, and if required, may be equipped with known aligning, guiding and forwarding means.